1. Field of the Invention
The present invention is directed in general to the field of integrated circuits. In one aspect, the present invention relates to a circuit and method of generating quadrature signals from a high-frequency input signal.
2. Description of the Related Art
Transceiver circuits are used in a myriad of wireless communication applications, such as cordless telephones, pagers, cellular telephones, and global positioning systems. With such transceiver circuits, quadrature modulation techniques are used which enable two independent signals to be combined at a transmitter, transmitted on the same transmission band, and separated at a receiver. The principle of quadrature modulation is that two separate signals, I and Q (In-phase and Quadrature phase), are modulated by using the same carrier wave frequency, but the carrier wave of signal Q is ninety degrees out of phase with the carrier wave of signal I. As a result, the quadrature modulated signals can be summed before transmission to the receiver. Because of the phase difference, the receiver can separate the summed I and Q signals from each other. In particular, the receiver typically receives a high-frequency input modulation signal from an antenna in a heterodyne system, and then downconverts the input signal to a much lower frequency using a mixer and a local oscillator signal. Once the incoming modulation signal is frequency shifted, the modulated data is recovered in the lower frequency signal. To convert the input high-frequency signal in a direct-conversion transceiver to a baseband frequency so that information in the input signal can be detected, quadrature signals are needed to apply to the mixer. Typically, quadrature signals are created by using divide-by-2 circuits, poly-phase filter or quadrature oscillator, but such solutions can increase the power consumption and required chip area, or otherwise require an oscillator that having a frequency that is twice the desired frequency. While self-calibrating quadrature generators have been proposed which use a delay locked loop (DLL) to produce quadrature outputs, these generators are used to generate quadrature signals in relatively low frequency (e.g., (<1 GHz) receivers. With higher frequency receivers (e.g., >10 GHz), it becomes more difficult to generate accurate quadrature signals because of variations in the process, voltage and/or temperature.
Accordingly, a need exists for an integrated transceiver circuit that generates accurate quadrature signals that may be applied to an image-reject mixer to convert the input high-frequency signal in direct-conversion transceiver to a baseband frequency signal. There is also a need for an improved receiver circuit to overcome the problems in the art, such as outlined above. Further limitations and disadvantages of conventional processes and technologies will become apparent to one of skill in the art after reviewing the remainder of the present application with reference to the drawings and detailed description which follow.